As well known, there have been developed various power generators which induce power generation. In those power generators, a permanent magnet member provided with permanent magnets arranged in the form of a tube and an electromotive coil member provided with electromotive coils arranged in the form of a tube are arranged concentrically. Namely, the single permanent magnet member and the single electromotive coil member are arranged concentrically. In this state, the single permanent magnet member is rotated to change magnetic force in the electromotive coil, and, thus, to induce power generation.
In the well-known power generator, since the magnetic force inducing power generation, that is, the magnetic force of the permanent magnet is constant, there has been employed the constitution as disclosed in Patent Document 1 in which an electromagnet is provided separately from the permanent magnet, and the magnetic force of the electromagnet is added or not added to increase or reduce the magnetic force.